Method and burner for burning powdered fuel



Jan. 5, 1932. R v. G. LEACH 1,839,535

METHOD AND BURNER FOR BURNING POWDEREDFUEL Filed Dec. 31. 1927 4 Sheets-Sheet l 227mm 6. (ya 0/:

Jan. 5, 1932. v. G. LEACH METHOD AND BURNER FOR BURNING POWDERED FUEL Filed Dec. 31. 1927 4 Sheets-Sheet V. G LEACH Filed Dec. 51, 1927 4 Sheets-Sheet 3 ya: I:

M63720)? 6 ea/ch WW 5 Jan. 5, 1932.

METHdD AND BURNER FOR BURNING POWDERED FUEL Jan. 5, 1932. v. G. LEACH 1,839,635

METHOD AND BURNER FOR BURNING POWDERED FUEL Filed Dec. 31, 192 4 Sheets-Sheet 4 HAIL-Ibv; l: Ve'mm @9072 Patented Jan. 5, 1932 UNITED STATES PATENT VERNON G. LEACH, OF CHICAGO, ILLINCIS METHOD AND BURNER FUR BURNING FOWDERED FUEL Application filed December 31, 1927.

\ burned more rapidly and uniformly than heretofore.

A further object of the invention is to provide means for adjusting the quantity of fuel burnt without impairing the operation of the burner.

Other and further objects of the invention will hereinafter appear.

A mixture of powdered fuel and air is selfcombustible and hence to avoid the flame striking back into the burner passages the velocity of the air through the latter must be greater than that of flame. propagation through said air charged with fuel. This involves relatively high muzzle Velocity at the burner.

To avoid furnaces of unnecessarily large length the flame should be short which means that the velocity of the streams of air and fuel should be checked and at the same time the particles of fuel should be burnt in a minimum length of time. r

The velocities of the air streams may be reduced by mutual impingement, the greater the angle betweenthe directions in which the streams are projected towards each other the greater is the reduction in velocity.

A suspension of powdered fuel in air is, however, not a homogeneous mixture like a mixture of two gases and centrifugal forces, as well as the kinetic energy of the particles 11 are to be considered. The impinging streamsof air carrying fuel are produced by splitting the original single stream and causing the split portions to flow around curved passages in the burner to give them the desired direction. In passing through these curved passages centrifugal force tends. to throw the fuel particles toward the outer wall of the passage and such particles as reach such wall move there alonguntildischarged into the furnace. Unless this outer mu has throughout its width a uniform radius in the plane of flow through the burner, the particles will tend to collect in the parthaving the greatest radius. Thus when Serial 1%. 243,838.

a burner is constructed with passages of circular cross-section, the particles moving along the outer wall of such passage will tend to collect along the center lines of the passages as these are the parts of greatest radius in the plane of flow through the burner. Gonsequently, there are projected from the burner two narrow concentrated streams of heavy fuel particles.

I have found that if the passages areof substantially rectangular cross-section, then, instead of a narrow concentrated stream of heavy particles, a stream the entire width of the burner is produced. Instead, therefore, of point concentration you have line concentration. v

Solong as the streams have to flow through curved passages immediately prior to dis charge, segregation of the particles towards the outer periphery of such particles isunavoidable. -However, I have found that so long as the thickness of the stream does not exceed about six inches, such segregation does not seriously interfere with combustion. However, in general, the stream should be as thin as practical and the necessary volume of air and fuel admitted should be obtained i by increasing the width of the burner.

It is also desirable that the distance the streams of air and fuel travel before mutual impingement should be short. Usually such distance should be only a small fractionrof the length of the resulting flame or, expressed in terms of burner construction, not less than four times the maximum thickness of the streams at the point of intersection.

- To get a short flame it is necessary to burn the particles of powdered fuel rapidly. This involves not merely an ample supply of oxygen for combustion but also rapid removal of the products of combustion from each particle; Ample supply of oxygen is ensured by avoiding too great segregation or concentration of the fuel particles. The rapid removal of the products of combustion from each particle is largely a matter of relatively velocity offuel particles and air. Inthe large majority of burners design ed for the use of finely divided fuel, the fuel is introduced into the furnace suspended, in a current of air,

both air and fuel having essentially the same velocity. Upon being introduced into the furnace, the fuel gives off its volatile content almost instantly, and this volatile content readily burns. The small particles of devolatilized fuel, however, soon surrounds themselves with an atmosphere of carbon monoxide or dioxide which has to be scrubbed off before further combustion can proceed. This scrubbing action is best brought about by the creation of a relative velocity between the fuel particle and the surrounding atmosphere of gases. Either tae fuel particles should travel faster than the gases, or the gases should travel faster than the fuel particles. If there is such relative movement of the particles and gas, the film of partially consumed gases which surrounds each fuel particle will be constantly scrubbed off and combustion will be completed in a short length of flame travel.

Now when the two streams of air and fuel meet, there is on the furnace side of each stream a layer of the heavier particles which have segregated out by centrifugal action within the burner. By the mutual impingement of'the two streams a single stream is produced moving towards the furnace and hence such resultant stream must either pass through such layers of heavier particles or, carry them along with it. Owing to their kinetic energy these particles to a large eX tent resist the forward urge of the resultant stream so that a relative movementof particle and gas is produced as is requisite for the de sired scrubbing actionj My improved method and burner for burn ing powdered fuel will be described in further detail in connection with the accompanying drawings which illustrate various forms V of construction. 7 i

In the drawings Figure 1 is a vertical section through a sterling boiler fitted with one of my improved burners.

Figure 2 is a side elevation of the burner.

Figure 3 is a plan view of the same.

Figure 4 is a front end view of the same.

Figure 5 is a sectionon the line VV of Figure 2. i V

Figure 6is a section on the line VI-VI of Figure 3.

Figure 7 is a section on the line VIL-VII of Figure 6. s

Figure 8 is a central longitudinal. section through another form of burn-er.

Figure 9 is a section on the line IXIX of Figure 8. V

Figure 10 is a central longitudinal section through still another form of burner. 'Figure 11 is a section on the line XI-XI of Figure 10. i

Figure 12 is a central longitudinal section through still another form of burner.

Figure 13 is a I section. on :the line XIIIXIII of F igure 12.

Figure 14 is a centrallongitudinal section through still another form of burn-er.

Figure 15 is a central longitudinal section through still another form of burner.

As shown on the drawings:

A complete installation is shown diagrammatically in Figure 1 including a sterling type boiler 1, burner 2 projecting through an orifice in the furnace or fire-box wall 3 and a blower and coal pulverizer l for supplying a stream of powdered coal suspended in air to the burner.

The burner, as shown in detail in Figures 2 to 6 inclusive, consists of a casing 5, flanged at its rear end for connection to a pipe 6 leading from the blower and pulverizer. T0- wards its front or furnace end the casing is rectangular in form and is provided with a series of lugs adapted to register with lugs 8 on two segmental cap pieces 9. The outer end of the casing 5 and the ends of the cap pieces 9 are flanged-inwardly, as at 10, for the reception of a tubular member 11. This tubular member 11 divides the stream of air into two parts and the curved outer walls of the cap pieces in conjunction with the member 11 direct these twoair streams inwardly towards each other at an angle of about 140. The two streams formed by the tubular member 11 are of-substantially rectangular cross-section and relatively wide and thin. The wide faces of said streams may be said to be in convergent planes (the planes tangent to the tubular member 11 or parallel thereto). Consequently, the impingement of said streams is along a line, or lines, formed by the intersection ofsaid planes.

The air pressure is such that the velocity of these two air streams as they issue from the burner is greater than the velocity of flame propagation in the air-fuel mixture. When, however, these two streams impinge they produce a fan-shaped stream in a plane perpendicular to the plane of symmetry passing through the longer axis of the tubular memaer 11. The velocity of the gases in this resultant stream is much lower than in its component streams and hence less than the velocity of flame propagation. As the velocity of the gases in this resultant stream is low, the flame is shortin spite of the fact that the gases issue from the burner at high velocity.

The greater the angle between the two component streams the slower will be the velocity of the resulting stream since the velocity, components of the two opposing streams in the direction of the resulting stream decreases as the angle referred to increases. Grdinarily, such angle should be more than 90 and for best results should be around 140.

hen the angle of impingement is around 140 there is a tendency for some of the mixture to be driven backwards against the burner instead of moving forward with the main body of flame. Thetubular member 11, however, acts as a splash plate and prevents rearward movement of the mixture although it does not actually contact with the flame. \Vhilc there is no flame contact there is considerable radiant heat transmitted to the tubular member 11 and this heat being carried around the latter by conduction is dissipated by heating the incoming air and fuel mixture. 7 i

In the same way the segmental portions 9 become heated by radiation from the flame and this heat is transmitted inpart to the casing and in part to the incoming air and fuel mixture. To aid in" the dissipation of heat to the incoming air the segmental members are formed with inwardly projecting fins 12. These fins taper inwardly and are made of streamlinecross-section in the direction of flow of the air (indicated by arrow in Figure 7), that is, are blunt where the air impinges and narrow and tapering where the air discharges, so as to impede the flow of air as little as possible.

'l/Vith the form of lmrner illustrated in Figures 1 to 7 inclusive the flow of air-fuel mixture can only be controlled by the supply means such as the blower and pulverizer. In other forms of burners, such as those illustrated in Figures 12 to 15 inclusive, the flow may be regulated by means within the burner, as will be described later.

The same principle of discharging the airfucl mixture in a stream of substantially uniform thickness is embodied in the constructions shown in Figures 8 to 11 inclusive, adapted to give annular and circular flames respectively instead of a fan-shaped flame.

In the burner shown in Figures 8 and 9 the casing is made annular in form so that a central passage 21 is provided for the entry of additional air. At its discharge end lugs are provided on the casing for attachment of annular members 22and 23 of segmental cross-section. The casing 20 and the member 22 are provided with inwardly extending fins 24a and 2 1 respectively. These fins have various functions, first to aid in heating the incoming air-fuel mixture. .Second, to support a ring 25 which serves to divide the air-fuel stream and then, in conjunction with members 22 and 23, deflects the two streams so formed towards each other to form a single flame of annular form. v

Third, these fins being located around the periphery only of the ring 25 serve to reduce the space around the outside of such ring for the passage of air sufiiciently to render such space equal to the spacearound the inside of such ring. In this way flow of air around the inner and outer portions of the ring 25 is equalized Another constructlon is shownin Fi ures construction analogous to those above de.

scribed, in that. the airotuel stream splitting members are ylindrical, annular and spherical respectively. The burners shown in Figures 12 to 15, however, are constructed so that the stream splitting members are adjustable relatively to the stream deflecting members so that the thickness of the streams of air and fuel discharged from the burner may be varied and varied uniformly throughout their entire length or width so as to decrease orincrease the size of the flame.

Controlling the size of flame by varying the thickness of theair-fuel streams means that the size of flame may be varied without great change in the muzzle velocity of the air leaving the burner. This enables the muzzle velocity to be maintained at. afigure not greatly in excess of that required to prevent the flames striking back into the burner.

A convenient method of securing this adjustment in connection with the cylindrical type of stream splitting member is shown in Figures 12 and 13. In this case the end of the casing 32 and the ends of the segmental members 33 are not cut away, as are the corresponding parts in the form shown in Fig: ure 2, but are arranged to form continuous flat surfaces over which the ends of the cylindrical stream splitting member 34: may slide. The member 34is guided in such movement by fins 35 and 36 which are formed with straight parallel inner edges spaced apart the diameter of the member 34. The position of the member 34: is controlled by a rod 37 passing rearwardly through the casing and a stuffing-box 38 in the elbow 39 connected by suitable piping to the air comressor and ulverizer. A handle such as 40 may beprovided for manual adjustment of the rod 37 and member 34.

In the form of construction shown in Fig ure 14 the ring 25 is rigidly connected to two adjusting rods 11. passing out through stufflng boxes 42 and provided with operating handles 43. As in the previous form of construction the stream splitting guided by inwardly extending and 45. I

The burner shown in Figure 15 is provided with a ball 29 adapted to slide between inwardly extending fins 4.6 and 47. This ball is furnished with an adjusting rod 48 passing through stufiing box l9 and provided with a handle 50.

I amaware that many changes may be member is fins, as 44:

made, and numerous details of construction may be varied through a wide range with-- out departing from the principles of this invention, and I therefore donot purpose limiting the patent granted hereon, otherwise than necessitated by the prior art.

I claim as my invention:

1. A burner for powdered fuel comprising a casing, connections at one end to a source of air under pressure, said casing having flat sides at the other end and an end portion of substantially cylindrical form extending transversely between said flat sides, said portion having a longitudinal slot centrally located therein for the dischar e of air and fuel, and a member within said casing extending between said flat sides in proximity to said slot and substantially uniformly spaced from the margins of said slot to divide the stream of air passing through the casing into two streams. V,

2. A burner as in claim 1 in which said member is movable towards and away from said slot to vary the flow of air through said burner.v

3. A burner for powdered fuel comprising a casing, connections at one end to a source of air under pressure carrying powdered fuel in suspension, an orifice at the other end of said. casing for discharging air carrying fuel into afurnace, a stream splitting member within said casing adjacent said orifice, the wall of the casing being curved around said member to cause the streams of air passing around said member to be projected towards each other at an angle greater than 90 for mutual impingement, and inwardly projecting iins onsaid casing adapted to contact with said stream splitting member to restrain movement of the latter transversely of the burner and allow movement longitudinally of the burner and means operable exteriorly of the burner for adjusting the position of said stream splitting member.

at. A burner for powdered fuel comprising a casing, connections at one end to a source of air under pressure carrying powdered fuel in suspension, an orifice at theotlierend of said casing for discharging aircarrying fuel into a furnace, a stream splitting mem ber within said casing adjacent said orifice, the wall of the casing said member to cause the streamsrof air passing around said member to be projected towards each other at an angle greater than 90 for mutual impingement, and inwardly pro ecting fins casing wall to aid in the transmission of heat to the air-fuel mixture flowing through the burner.

5. A burner for powdered fuel, comprising 'a casing having an elongated terminal 7 7 slot for the'dischargeof the fuel and air, a

member cooperable'with sides of the casing positioned w-1th1n said caslng substantially being curved around on the curved portion of said uniformly spaced from and in proximity to the margins of sand slot to dlvide the stream of fueland air passing through the casing spaced therefrom and from the edges of said elongated opening.

7..A burner for powdered fuel comprising a casing having curved walls defining a single relatively narrow, elongated terminal opening for the discharge of a stream of mixed fuel and air and a. member within saidcasing conforming in contour with the portions of said curved walls adjacent said opening, said member cooperating with said walls to divide said stream into two convergent stream prior to discharge through said opening.

- 8. A burner for powdered fuel comprising a casing having curved walls defining a single relatively narrow, elongated opening for the discharge of a stream of mixed fuel and air, a member within said casing conforming in contour with theportions of said curved walls adjacent said opening, said member serving to divide said stream into two convergent streams prior to discharge through said opening and means for moving said member relative to said opening to adjust the thickness of the air-fuel stream discharged.

9. A burner for powdered fuel, comprising a casing having opposed curved walls and intermediate plane walls defining a single relatively narrow, elongated opening for the discharge of a fuel-air mixture, a stream splitting member positioned within said casing adjacent said opening and contacting said plane walls at its ends, said member conforming in contour with the curvature of said curved walls to divide said air-fuel mixture into two convergent streams for discharge through said opening. 1

10. A burner for powdered fuel, comprising a casing having curved walls terminating in opposed edges to form a discharge opening therebetween for a fuel-air mixture anda stream splitting member within said casing adjacent said opening having walls conforming with the curvature of said casing walls and substantially uniformly spaced therefrom toward said opening, said member serving to divide the'air-fuel mixture into two convergent streams for discharge through said opening.

11. A burner for powdered fuel, comprising a casing having curved walls terminating in opposed edges to form a discharge opening therebetween for a fuel-air mixture, a stream splitting member within saidcasing adjacent said opening having walls conforming with the curvature of said casing walls and substantially uniformly spaced therefrom toward said opening, said member serving to divide the air-fuel mixture into two convergent streams for discharge through said opening and fins extending inwardly from said curved casing walls into contact with said member.

12. A burner for powdered fuel, comprising a casing having coaxial curved walls providing an annular passage for a fuelair mixture and an inner passage for additional air, said walls terminatin in arelatively narrow annular opening for thedischarge of said fuel-air mixture and a toroidal member within said casing adjacent said opening for dividing the fuel-air mixture charging said stream, and igniting said mixture.

In testimony whereof I have hereunto subscribed myname.

VERNON G. LEACH.

into two annular streams for discharge through said opening. I

13. A burner for powdered fuel, comprising a casing having coaxial curved walls providing an annular passage for a fuel-air mixture and an inner passage for additional air, said walls being transversely curved at one end and terminating in opposed edges to define a relatively narrow annular opening for the discharge of said fuel-air mixture and a toroidal member within said casing adj acent said opening for dividing the fuel-air mixture into two annular convergent streams for discharge through said opening.

14. A burner for powdered fuel,comprising a casing having coaxial curved walls providing an annular passage for a fuel-air mix ture and an inner passage for additional air, said walls terminating in a relatively narrow annular opening for the discharge .of said fuel-air mixture, a toroidal member within said casing adjacent said opening for dividing the fuel-air mixture into two annular streams for discharge through said opening and means for adjusting the position of said member relative to said opening.

15. In a burner for powdered fuel, a burner casing having an elongated terminal opening, and a member axially movable in said casing and positioned adjacent said opening, said member being arranged cooperable with the terminal portion of said casing to divide the fuel stream into two parts.

16. The method of burning powdered fuel while suspended in a combustible mixture of fuel and air, which method comprises splitting a main stream of the mixture into two similarly curved relatively wide thin streams, causing said streams to mutually impinge to form a resulting stream, then dis- 

